Integrated circuits (ICs) comprising many tens of thousands of semiconductor devices including field effect transistors (FETs) are a cornerstone of modern microelectronic systems. The various regions of the FETs (e.g. source/drain and source/drain extensions) are formed by introducing dopant atoms into a semiconductor substrate using methods such as ion implantation and indiffusion. After the dopants have been introduced, they are electrically activated by subjecting the semiconductor substrate to one or more anneal processes such as low temperature thermal anneal, rapid thermal anneal, spike anneal, flash anneal or laser anneal.
Unfortunately, during the anneal process, the dopants have a tendency to diffuse or expand both laterally and vertically away from the profile as-introduced thereby increasing the dimensions of the various device regions. This diffusion is undesirable particularly as semiconductor devices are scaled down in size.
For example, as the gate length of FETs is scaled down for example to 45 nm and beyond, the source and drain regions increasingly interact with the channel and gain influence on the channel potential. As a result, the gate electrode has reduced control over the on and off states of the channel. This effect is known as the short channel effect. In order to reduce the short channel effect, it is desirable to fabricate MOS devices with shallower source/drain extension and/or source/drain junctions and also reduce the lateral extension of the source/drain extension and/or source/drain regions after anneal.
In addition to the above, the level of dopant activation is also a critical factor as device dimensions are scaled down. This is because the resistance of the various regions e.g. source/drain (S/D) region increase as they are shrunk in size. Since an increase in the level of dopant activation leads to a decrease in resistance, a higher level of dopant activation is desirable.
In view of the above discussion, there is a need for fabrication techniques that can at least partly mitigate the problems of limiting extent of dopant diffusion and increasing the level of dopant activation.